Automatic test equipment (ATE) refers to an automated, usually computer-driven, system for testing devices, such as semiconductors, electronic circuits, and printed circuit board assemblies. A device tested by ATE is referred to as a device under test (DUT).
ATE is capable of providing different types of signals to a DUT. Among these signals are test signals, which are used to test the DUT. The test signals may be analog signals that are generated based on digital signals received from a computer or other processing device. A digital-to-analog converter (DAC) (or several DACs) in the ATE is typically used to perform conversion(s) from digital to analog.
A DAC produces an analog signal by sampling a digital signal. A DAC may sample the digital signal using one edge of a clock—the rising or falling edge—or both edges of the clock. Sampling using both edges means that the digital signal is sampled at both the rising and falling edges of the clock. This type of sampling produces a higher sampling rate, and thus a more accurate analog signal. Sampling using both edges of the clock, however, can be quite sensitive to duty cycle errors in the clock.
The duty cycle of a clock is a ratio of the amount of time that the clock is high to the time of one clock cycle. In some systems, an error in the duty cycle occurs if the ratio is anything other than 50%, meaning that the clock is high half of the time and low half of the time. For DACs that sample using both edges of the clock, an error in the duty cycle can result in frequency spurs in output analog signals.